Key for coding mask must be exactly & places long

What causes this issue?

The length of the key for the coding of the project definition or the
WBS element is not correct. You defined the length of the key to be
exactly "&V1&" characters long.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Enter a key with the correct length.
INCLUDE 'NA_ALLG_VORGEHEN' OBJECT DOKU ID TX
Check if the indicator for the key for the project coding was correctly
defined. Change it if necessary.

Error message extract from SAP system. Copyright SAP SE.